1. Field of the Invention
The present invention is directed to an X-ray apparatus of the type having a radiation source, an interchangeable radiation filter and an area dose measuring device with a measurement chamber and an allocated evaluation device for determining the area dose product on the basis of the measured signals provided by the measurement chamber, with the measurement chamber arranged preceding the filter in the beam path with reference to the radiation propagation direction.
2. Description of the Prior Art
Measurement of the area dose product allows determination of the amount of X-radiation applied to the examination subject, for example a patient. This measurement is conventionally undertaken with an area dose-measuring device having a measurement chamber that is arranged in the beam path. This measurement chamber usually is an ionization chamber through which the X-rays pass and at which an output signal dependent on the amount of radiation can be obtained. The applied, surface area-dependent dose can be determined from this signal, usually in μGym2 units.
Radiation filters are often employed in known X-ray apparatuses in order to attenuate or entirely blank the X-rays in certain filter-specific ranges. A large variety of interchangeable and employable filters are known, for example shoulder filters, foot filters, pelvis filters or skull filters. These filters, that are usually fashioned in the form of essentially rectangular plates, are inserted into the beam path. These insertion guides usually are arranged outside the housing containing the measurement device and further parts of the area dose-measuring device, such as, the evaluation device. The measurement chamber lies in front of the filter with reference to the radiation propagation direction. The measurement chamber often is integrated into a diaphragm device that follows the radiation source in the propagation direction, particularly in the depth diaphragm, and which has an outer housing section at which the insertion guides for the plate-like radiation filters are located.
Due to this arrangement wherein the radiation filters follow the measurement chamber, the problem arises that the filter effect does not enter into the determination of the area dose product. The filter performance that attenuates the X-rays that are actually applied to the subject is not taken into consideration since the measurement occurs preceding the radiation filter. Ultimately, thus, the applied dose is lower than that indicated by the “unfiltered” measured result.